1. Field of the Invention
The present invention relates to methods and apparatus for transferring wafers from wafer carriers to wafer conveyor apparatus in surface treatment apparatus of so-called carrierless systems for removing laminate-like wafers such as semiconductor substrates (hereinafter referred to as wafers) from wafer carriers and treating surfaces thereof. For example, the present invention relates to a method and apparatus for wet treatment in which a number of wafers are dipped into a treatment bath containing a surface treatment solution as an etching solution, a film removing solution, a developing solution or a cleaning solution, or an apparatus for vapor treatment in which vapor of such a treatment solution is supplied to a number of wafers inside a treatment bath for treating the same with the vapor.
2. Description of the Related Art
With development in semiconductor technology having reached a high level, techniques for maintaining high wafer quality are required in the wafer manufacturing process. Presently used in the surface treatment of wafers is a carrier batch system and a carrierless system. In the carrier batch system, wafers are transferred from a conveyor carrier to a surface treatment carrier and then the wafer surfaces are treated. In the carrierless system, wafers are treated without being stored in a carrier during surface treatment. Both of these systems are intended to prevent dust from contaminating the surface treatment bath.
The carrierless system has a larger number of advantages as compared to the carrier batch system. For example, in the carrierless system, dust attaching to a carrier is never brought into a surface treatment bath. Accordingly, contamination of the surface treatment solution is reduced. The amount of the treatment solution which is brought out of the treatment bath decreases to reduce the amount of the solution that is consumed. Some of the treatment solution which is brought out of the treatment bath and is returned to the bath to prevent degradation of the treatment solution. Furthermore, in the carrierless system, dead space inside a wafer dipping tank is smaller because it does not use a carrier. Accordingly, the surface treatment apparatus can be reduced in size. The unit cost of space of a clean room in which a surface treatment apparatus is provided is high, so that the cost of the entire system can be reduced if the apparatus can be smaller. Furthermore, since a smaller capacity tank can be used, the treatment solution can be saved to facilitate management of the solution.
Such known carrierless systems include one disclosed in Japanese Utility Model Laying-Open No. 2-47046.
Referring to FIGS. 1 and 2 herein, wafer chuck 115 of a wafer conveyor apparatus (a wafer conveyor robot) used in the system disclosed in Japanese Utility Model Laying-Open No. 2-47046 includes a pair of parallel arms 118, and chuck hands 19 provided facing each other on lower portions of inner surfaces of arms 118 for holding a wafer W. A number of grooves 119a are formed in respective chuck hands 119 for accommodating wafers W and supporting wafers W from underneath.
In order to treat a number of wafers in a single surface treatment, a sufficient number of grooves 119a (FIG. 2) for holding wafers stored in two wafer carriers are formed in chuck hands 119. Grooves 119a are formed separately in two regions in each chuck hand 119 corresponding to each of wafer carriers as shown in FIG. 2.
Operation of the system disclosed in Japanese Utility Model Laying-Open No. 2-47046 includes a step of positioning two wafer carriers each accommodating a plurality of wafers such that the surfaces thereof are vertical and peripheries of respective wafers are aligned so that wafer alignment directions thereof coincide with each other, a step of engaging wafers inside respective wafer carriers with two wafer holding members to hold them together respectively, a step of holding together the wafers held by two wafer holding members with wafer chuck 115 shown in FIGS. 1 and 2, and a step of conveying the wafers held by wafer chuck 115 into a surface treatment apparatus.
In this case, an interval or space between the wafer carriers is larger than an interval between wafers stored in respective wafer carriers. Accordingly, grooves 119a of chuck hands 119 had to be formed in two regions corresponding to respective wafer carriers as shown in FIG. 2.
In the system disclosed in Japanese Utility Model Laying-Open No. 2-47046, wafers for two carriers can be collectively subjected to surface treatment being held by wafer chuck 115. Therefore, the efficiency of surface treatment increases as compared to surface treatment in which wafers for a single carrier are treated individually. In this case, however, as clearly seen from FIG. 2, the interval between wafer groups of each wafer carrier is larger than the intervals between respective wafers in a group. The efficiency of circulating a treatment solution inside a surface treatment bath varies in a portion of a large interval as compared with a portion of a narrow interval. Therefore, the surface treatment of wafers at both ends of each wafer group is not the same as the surface treatment of wafers provided in other portions. Such uneven surface treatment has to be avoided.
Such a method of transferring wafers as described above is also used for another prior art method that includes a step of positioning two wafer carriers accommodating a plurality of wafers in a standing and aligned manner so that the directions of aligning wafers are the same, a step of collectively holding the wafers inside each wafer carrier with such a wafer chuck 115 as shown in FIG. 2, and a step of transferring the wafers W held by wafer chuck 115 to a wafer holding member 121 (FIG. 3) previously positioned inside a surface treatment bath 120. In this method the wafers W are held inside a treatment solution S in a standing and aligned manner by wafer holding member 121.
Such a system also has a similar problem as that of the system disclosed in Japanese Utility Model Laying-Open No. 2-47046. Referring to FIG. 3, a relatively large space S.sub.1 is formed between a wafer group W.sub.1 from a first wafer carrier and a wafer group W.sub.2 from a second wafer carrier. Also, relatively large space S.sub.2 are formed between the wafer group W.sub.1 and a wall surface of a treatment bath 120 and between the wafer group W.sub.2 and a wall surface of treatment bath 120. On the other hand, relatively small spaces S are formed among wafers w included in each of wafer groups W.sub.1 and W.sub.2. The flow of the surface treatment solution changes according to the intervals among wafers. Accordingly, the surface treatment of wafers W will not be homogeneous corresponding to positions where wafers are located, that is, end portions of wafer groups or other portions.
Also, the prior art has a problem that a volume of surface treatment bath 120 is large. This is because the space S.sub.1 between wafer groups W.sub.1 and W.sub.2 is unnecessarily large. Accordingly, an area required for provision of a surface treatment apparatus including a surface treatment bath and the like is large, and a greater quantity of surface treatment solution is required. Such problems as described above are encountered not only in the equipment for wet treatment but also in the equipment for vapor treatment.